Air blower

ABSTRACT

An air blower is provided with a drive motor and an air blowing fan which has a hub mounted to the drive motor and blades which are provided to the hub. The air blower is characterized in that serrations comprising triangle-shaped protrusions are provided to the front edge of each of the blades so as to be arranged along the front edge and in that the pitch, the height, or the direction of the serrations is changed according to the flow of air at a radial position on the air blowing fan.

TECHNICAL FIELD

The present invention relates to an axial flow blower, centrifugalblower, diagonal flow blower, etc., more particularly relates to astructure of a fan blade which can suppress disturbances in the air flowand reduce noise.

BACKGROUND ART

Better blower performance and lower noise are being sought from axialflow blowers etc. PLT 1 discloses providing a plurality of triangularshape projections in a sawtooth manner (hereinafter referred to as“serrations”) in a chord line direction with an all leading edge part ofeach blade to reduce the noise of rotation due to the blower fan.

In general, the flow of air near a blade surface of a blower greatlydiffers depending on the part. The further to the outer circumferenceside in the radial direction of the blower fan the blower fan is, thehigher the flow rate is. Further, the direction of the air flow at theouter circumference side of the blower fan, with respect to thedirection of rotation, greatly changes depending on the design of theblade (forward curved blade or backward curved blade). That is, in aforward curved blade (forward swept wing), the flow becomes an axialflow which concentrates at the blade center, while in a backward curvedblade (sweptback wing), the flows becomes a slanted flow which headstoward the blade outer circumferential direction. Furthermore, at theblade end part, a back flow also occurs from a positive pressure surfaceto a negative pressure surface side. In such a prior art as PLT 1,serrations which were provided with a blade could not sufficientlysuitably deal with changes in the flow of air depending on the portionof the blade and a sufficient noise reduction effect sometimes could notbe obtained. Further, a drop in the air flow was sometimes caused or thedrive torque increased and a drop in efficiency was caused.

CITATIONS LIST Patent Literature

PLT 1: Japanese Unexamined Patent Publication No. 2000-087898

SUMMARY OF INVENTION Technical Problem

The present invention, in consideration of the problem, provides ablower which prevents a drop in the air flow while effectively reducingthe fan noise.

Solution to Problem

To solve the problem, an aspect of the invention of claim 1 provides ablower comprising a drive motor and a blower fan having a hub which isattached to the drive motor, and a plurality of blades which areprovided at the hub, wherein the blades are provided at their bladeleading edge parts with serrations comprised of pluralities oftriangular shape projecting parts along the blade leading edge parts andthe serrations are changed in pitch, height, or direction according tothe flows of air at radial direction positions of the blower fan.

To solve the problem, an aspect of the invention of claim 10 provides ablower fan having a hub which adapts to be attached to a drive unit, anda plurality of blades which are provided at said hub, wherein

each said blade has a first portion of a blade leading edge part of saidblade which has a first distance in the radial direction from the centerof rotation of said blade, and a second portion of a blade leading edgepart of said blade which has a second distance in the radial directionfrom the center of rotation of said blade, said blade leading edge partis provided with a plurality of serrations which stick out to anupstream side of flow of air, wherein said serrations have first slantedsides which are slanted with respect to a direction of flow of air, andsecond slanted sides which are slanted in a different direction fromsaid first slanted sides with respect to a direction of flow of air, andat least one of a pitch, height, and direction of said projections atsaid first portion differs from at least one of a pitch, height, anddirection of said projections at said second portion.Note that the parenthesized reference notations show the correspondencewith specific examples which are described in the later mentionedembodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front schematic view of a first embodiment of the presentinvention.

FIG. 2 is a schematic view of a blade of a first embodiment of thepresent invention.

FIG. 3 is a view of one example of the results of simulation analyzingthe structure of the flow around leading edge serrations by CFD(computational fluid dynamics).

FIG. 4 is an explanatory view of the results of simulation of FIG. 3.

FIG. 5 is a cross-sectional view of a blade of the simulation of FIG. 3.

FIG. 6A is an explanatory view for explaining a general axial flowblower.

FIG. 6B is a cross-sectional view developed along the line A-A of FIG.6A.

FIG. 6C is an explanatory view for explaining a positive pressuresurface and a negative pressure surface of a blade of FIG. 6B.

FIG. 7 is a schematic view of a blade of a second embodiment of thepresent invention.

FIG. 8 is a schematic view of a blade of a third embodiment of thepresent invention.

FIG. 9 is a schematic view of a blade of a fourth embodiment of thepresent invention.

FIG. 10 is a schematic view of a blade of a fifth embodiment of thepresent invention.

FIG. 11 is a schematic view of a blade of a sixth embodiment of thepresent invention.

FIG. 12 is a schematic view of a blade of a seventh embodiment of thepresent invention.

FIG. 13 is a schematic view of a blade of an eighth embodiment of thepresent invention.

FIG. 14 is a schematic view of a blade of a ninth embodiment of thepresent invention.

DESCRIPTION OF EMBODIMENTS

Below, referring to the figures, embodiments of the present inventionwill be explained. In the embodiments, parts configured the same will beassigned the same reference notations and explanations will be omitted.

First Embodiment

Referring to FIG. 1, a blower 10 is a so-called electric blowercomprising a blower fan 1 which is placed in a shroud 200 and which isdriven to rotate by a drive motor (electric motor) 300. The blower 10 isfastened to an engine side of an automobile radiator by mounts 250 whichare provided near the four corners of the shroud 200 and blows air forcooling use to the core part of the radiator. The outside shape of theshroud 200 forms a rectangular shape corresponding to the core part ofthe radiator. At the approximate center, a ring-shaped shroud ring part210 is formed so as to encircle the blower fan 1 by its outercircumference. This shroud ring part 210 is provided at the shroud 200so as to be positioned at the outside of the ring 2 of the blower fan 1in the radial direction. There may also be no ring 2 of the blower fan 1in the present embodiment. The blower 10 and the later explained blades3 of the present invention are not limited to use for an automobileradiator. They are may be used for general industrial use. Theexplanation will mainly be given for an axial flow blower, but similareffects can be obtained even for a centrifugal blower, diagonal flowblower, and cross-flow blower. The drive motor 300 is not necessarilylimited to an electric motor.

Between the shroud ring part 210 and the rectangular shape outercircumference part of the shroud 200, an air conduit 220 is formed whichexpands toward the upstream side of air of the blower fan 1. At thecenter of the shroud ring part 210, a circular motor holding part 230 isformed. This motor holding part 230 is supported by a plurality of motorstays 240 which extend radiately to the outside in the radial directionand are connected to the shroud ring part 210. At the motor holding part230, an electric motor 300 is fastened. The shaft of the electric motor300 and the hub 4 of the blower fan 1 (see FIG. 2) are fastened. Theblower 10 comprises this blower fan 1, electric motor 300, etc. The hub4 of the blower fan 1 is cylindrical in shape and is provided with aplurality of blades 3 in the radial direction.

Parameters of the blades 3 such as the chord line C, positive pressuresurface, negative pressure surface, angle of attack a, lift, etc. arethe same as the general definitions such as shown in FIGS. 6A to 6C.Further, a blade shape where the blade end part at the outercircumference side is curved backward in the direction of rotation ofthe blower fan 1 will be called a “backward curved blade”, while a bladeshape where the blade end part at the outer circumference side is curvedforward in the direction of rotation of the blower fan 1 will be calleda “forward curved blade”. At the blade leading edge part of the blade 3,a plurality of serrations (triangular shape projecting parts) areformed. The serrations have first slanted sides 3 a which are slantedwith respect to the direction of flow of air and second slanted sides 3b which are slanted in a different direction from the first slantedsides 3 a with respect to the direction of flow of air (see FIG. 7). Inthe triangular shape projecting parts which form the serrations, here,the bottom side of the triangular shape projecting part will be calledthe “pitch p” of the serrations (triangular shape projecting parts), theline segment bisecting the vertex a of the triangular shape projectingpart will be called the “direction” of the serrations (triangular shapeprojecting parts), and the distance of the bisecting line segment of thevertex to the bottom side will be called the “height h” of theserrations (triangular shape projecting parts). The larger “size” of theserrations (triangular shape projecting parts) indicates the larger ofthe pitch or height of the serrations. The vertexes a of the triangularshape projecting parts are called vertexes a of the serrations. In thecase where the sides of the triangular shapes are curved, the shapes aregenerally based on these.

First, to start, the effects of the serrations which form the basis ofthe present invention will be explained. The simulation of FIG. 3 is thecase where the triangular shape projecting parts of the serrations arethe same shapes in the direction of the blade leading edge. FIG. 3 is aview of a blade leading edge as seen from an upper position. The arrowmarks which are shown in FIG. 3 show projections of the tangentialvelocity of the flows around the serrations on the projection plane ofthe X-Z plane (S plane of FIG. 4). A flow from the valley parts at thetwo sides to the top surface of a peak part can be seen as occurring. Atthe serrations, first, at the tip parts of the peaks, small vortexesoccur. These grow to large vortexes further toward the valleys. Further,backward the peaks, it is believed that downward flows occurred by thevortexes, press down the flow separation, which particularly easilyoccurs at the negative pressure surface with the large flow rate, andtherefore reduce the flow separation. Due to this, the disturbances nearthe blade surface are eased and the fluctuation of pressure at the bladesurface is suppressed, so it becomes possible to obtain an effectleading to lower noise.

The first embodiment of the present invention is an embodiment changingthe pitch, height, or direction of the serrations according to the flowof air at the radial direction position of the blower fan 1, in order toutilize the above basic effect of the serrations. That is, the firstembodiment differs in at least one of the pitch, height, and directionof serrations in the first portion and second portion which aredifferent in distance in the radial direction of the blower fan from thecenter Q of rotation of the blade 3. As one example of the first portionand second portion of the blade 3, parts differing in the flow rate ofair (flow rates of FIGS. 7 and 8) and directions of flow etc. may bementioned. However the invention is not limited to these portions, butportions of any two locations along the blade 3. The flow of air nearthe blade surfaces of the blower greatly differ depending on theportion. The nearer to the outer circumference side in the radialdirection of the blower fan the portion of the blade is, the higher theflow rate is. Further, at a forward curved blade, the flow becomes anaxial flow which concentrates at the blade center, while at a backwardcurved blade, the flow becomes a diagonal flow which heads toward theouter circumferential direction of the blade. Furthermore, at the bladeouter end part, a back flow arises from the positive pressure surface tothe negative pressure surface. Changing the pitch, height, or directionof serrations in accordance with the flow of air at radial directionpositions of the blower fan 1 (at least two locations) is extremelyimportant in reducing the flow separation. Due to this, the basic effectof the serrations is exhibited, disturbances near the blade surfaces areeased, and pressure fluctuations at the blade surfaces are suppressed,so it becomes possible to obtain an effect leading to lower noise.

The first embodiment is a fan which is characterized by providing flowcontrol shapes which minimize the noise which is produced due todisturbance of the air at different positions of the blades. Due to theflow control shapes, the effect is obtained of both noise reduction andprevention of a drop in the air flow and increase of the drive torque.The blades have serration shape (sawtooth teeth) portions. The serrationshapes are changed according to the flow of air. According to this, itis possible to suitably set the serration shapes at the individualportions which differ in direction of air flow and flow rate, so it ispossible to realize the effect of both noise reduction and theprevention of both a drop of the air flow and increase of the drivetorque.

Second and Third Embodiments

The second and third embodiments are embodiments corresponding to thecase where the air near a blade surface of the blower flows in thecircumferential direction of the blower fan. The second embodiment, asshown in FIG. 7, is characterized in that the further to the bladeoutside diameter side the blade is, the larger the sizes of theserrations are made. The serrations are directed toward thecircumferential direction of the blower fan. According to this, the sizeof the serrations is increased at the portion with a large flow rate atthe blade outer circumference side, and the whirled air flow which isformed at the serrations, becomes weaker at a portion further toward theblade inside circumference side and becomes stronger at a portionfurther toward the blade outer circumference side. Due to this, at theflow with a high flow rate where flow separation would easily occur, itis possible to form a downward flow toward the blade surface and reducethe flow separation to obtain the effect of both noise reduction and theprevention of a drop in the air flow and increase of the drive torque atthe blade as a whole.

The third embodiment, as seen in FIG. 8, is characterized in that thefurther to the blade outside diameter side the blade is, the more acutethe vertices a of the serrations is. According to this, the serrationangle is made acute at the portion of the large flow rate at the bladeouter circumference side, and the whirled air flow which is formed atthe serrations becomes weaker at a portion further to the blade insidecircumference side and becomes stronger at a portion further to theblade outer circumference side. Due to this, at the flow with a highflow rate where flow separation would easily occur, it is possible tostrengthen the downward flow at the blade surfaces formed at theserration valley parts in order to achieve both noise reduction, andprevention of both a drop in air flow and increase in drive torque inthe blade as a whole. The invention is not limited to the case of makingthe pitch p of the serrations constant and increasing the height h ofthe serrations to make the angle acute. It is also possible to make theserration angle acute, regardless of the length of the bottom sides ofthe triangular shaped projections, at the portions with a large flowrate at the blade outer circumference side.

Fourth Embodiment

The fourth embodiment, as seen in FIG. 9, is characterized in that theblade trailing edge 7 is also provided with serrations and in that theblade leading edge 6 and blade trailing edge 7 are changed in serrationshapes. When the blade trailing edge 7 is provided with serrations,since the flow at the high pressure blade positive pressure surface andthe flow at the low pressure blade negative pressure surface are mixednear the blade trailing edge, the flows of the two surfaces graduallycross due to the serrations, so it is possible to suppress thedisturbances in the flow of air of the blade trailing edge. The bladeleading edge 6 and the blade trailing edge 7 may be suitably set withserration shapes. If the blade trailing edge 7 is made smaller in sizeof serrations compared with the blade leading edge 6, the serrations atthe blade leading edge side, which are provided for suppressing flowseparation, can be made larger so as to form a radiated flow. On theother hand, the serrations at the blade trailing edge side, which areprovided for suppressing disturbances of the air flow, can be madesmaller so as to make the flows at the positive and negative pressuresurfaces gradually cross. Therefore, the effect is obtained of bothnoise reduction, and the prevention of both a drop in the air flow andincrease of the drive torque. It is also possible to change the range ofprovision of serrations between the blade trailing edge and the bladeleading edge, and possible to provide serrations at only suitablepositions of the blade leading edge 6 and blade trailing edge 7.

In the following fifth and sixth embodiments, embodiments are explainedwhich correspond to the case where the flow of air near the bladesurfaces of the blower is a diagonal flow slanted with respect to thecircumferential direction of the blower fan.

Fifth and Sixth Embodiments

The fifth embodiment, as shown in FIG. 10, is an embodimentcorresponding to the case where the flow of air near the blade surfacesof the blower is a diagonal flow. The fifth embodiment matches thedirection of the serrations of the blade leading edge with the directionof diagonal flow. The sixth embodiment, as shown in FIG. 11, ischaracterized by changing the range of provision of serrations betweenthe blade trailing edge 7 and the blade leading edge 6. For example,when the air flow becomes a diagonal flow such as with a backward curvedblade, the air flows on the blade surface in the direction to the outercircumference, from the blade leading edge 6 toward the blade trailingedge 7. At this time, at the blade leading edge side where there isinterference with the air flow at all positions of the blade, serrationsare provided over a wide range, while at the blade trailing edge side,serrations are provided at only the parts with remarkable diagonal flow,so noise reduction and prevention of a drop of air flow and increase ofdrive torque can both be realized.

The following seventh and eighth embodiments are embodimentscorresponding to the case where the flow of air near the blade surfaceof the blower is a back flow from the positive pressure surface of theblade end part to the negative pressure surface side.

Seventh and Eighth Embodiments

The seventh embodiment, as shown in FIG. 12, is characterized by makingthe serration shapes of the blade end part smaller. According to this,the serration shapes are made smaller at the blade end part where thedisturbance of the air flow due to the back flow is large, so the swirlof the air flow formed at the serrations is subdivided. Due to this, thedisturbance of the air flow at the blade end part can be reduced, so theeffect is obtained of noise reduction, and prevention of both a drop inair flow and increase of drive torque. The eighth embodiment, as shownin FIG. 13, is characterized by making the serration shapes of the bladeend part at the blade trailing edge 7 smaller. Operational effectssimilar to the seventh embodiment are obtained.

Ninth Embodiment

The ninth embodiment, as shown in FIG. 14, is an embodiment which makesthe direction of the serrations of the blade leading edge 6 match thedirection of diagonal flow and makes the serration shapes of the bladeend part match the air flow due to the back flow, so as to deal with theflow of air near the blade surface of the blower. The ninth embodimentis included in the first embodiment. According to this, it is possibleto set the direction of the serrations to match the direction of flow,so the effect is obtained of noise reduction, and prevention of both adrop in air flow and increase in drive torque. Of course, combinationsof the fifth and sixth embodiments for the diagonal flow and the seventhand eighth embodiments for the back flow is included in the ninthembodiment. The present invention was described with reference tospecific embodiments selected in accordance with the purpose ofillustration, but it is clear that a person skilled in the art couldconceive of numerous modifications without departing from the basicconcept of the present invention and scope of disclosure of the same.

REFERENCE SIGNS LIST

-   -   1 blower fan    -   3 blade    -   4 hub    -   300 drive motor

What is claimed is:
 1. A blower comprising a drive motor and a blowerfan having a hub which is attached to said drive motor, and a pluralityof blades which are provided at said hub, wherein said blades areprovided at their blade leading edge parts with serrations comprised ofpluralities of triangular shape projecting parts along the blade leadingedge parts and said serrations are changed in pitch, height, ordirection according to the flows of air at radial direction positions ofsaid blower fan.
 2. The blower according to claim 1, wherein saidserrations have a pitch or height which becomes larger as the serrationsare further to the blade outside diameter side.
 3. The blower accordingto claim 1, wherein said serrations have an angle of vertices whichbecomes smaller as the serrations are further to the blade outsidediameter side.
 4. The blower according to claim 1, wherein saidserrations have a direction in the circumferential direction of theblower fan.
 5. The blower according to claim 1, wherein said serrationshave a direction in the direction of flow of air other than thecircumferential direction of the blower fan.
 6. The blower according toclaim 1, wherein said serrations have a pitch, height, or direction madea magnitude or a direction corresponding to a back flow at the blade endpart.
 7. The blower according to claim 1, wherein said blades have ablade trailing edge part with serrations comprised of a plurality oftriangular shape projecting parts along the blade trailing edge part. 8.The blower according to claim 7, wherein said serrations of said bladetrailing edge part have a pitch or height smaller than said serrationsof said blade leading edge part.
 9. The blower according to claim 7,wherein said serrations of said blade leading edge part and saidserrations of said blade trailing edge part are different in setposition in radial direction position of the blower fan.
 10. A blowerfan having a hub which adapts to be attached to a drive unit, and aplurality of blades which are provided at said hub, wherein each saidblade has a first portion of a blade leading edge part of said bladewhich has a first distance in the radial direction from the center ofrotation of said blade, and a second portion of a blade leading edgepart of said blade which has a second distance in the radial directionfrom the center of rotation of said blade, said blade leading edge partis provided with a plurality of serrations which stick out to anupstream side of flow of air, wherein said serrations have first slantedsides which are slanted with respect to a direction of flow of air, andsecond slanted sides which are slanted in a different direction fromsaid first slanted sides with respect to a direction of flow of air, andat least one of a pitch, height, and direction of said projections atsaid first portion differs from at least one of a pitch, height, anddirection of said projections at said second portion.